1. Field of the Invention
This invention relates to a process for the manufacture of a heat exchanger or heat transfer element. It is concerned with the kind having a metal tube which contains a porous body metalically connected with the wall of the tube. The porous body is made of polycrystalline metal whiskers or metallised non-metal threads inserted loosely into the tube, or it may be in the form of a porous skeleton consisting of such whiskers or threads and insertable as a single member into the tube. The metallic connection is effected by depositing metal by means of the thermal decomposition of a metal compound.
2. Brief Description of the Prior Art
A heat transfer element representative of the prior art is described for example in published German Specification No. 2157807.
Heat exchanger or heat transfer elements of this kind are normally arranged to have a heat-absorbing and/or a heat-releasing liquid or gaseous medium flowing through a porous body disposed in a tubular member, while the tube wall acts as a constructional element which gives off or takes up heat. In every case it is of importance to obtain a speedy heat exchange or transfer, and this means that the porous body should have a very good heat conducting connection with the tube wall. This connection is produced by the deposition of metal by means of the thermal decomposition of a metal compound. The tube with the whiskers, threads or skeleton is heated to the decomposition temperature of the appropriate metal compound and this metal compound is passed through the tube. Metal deposition takes place not only in the area of contact of the whiskers, threads or skeleton with the tube wall, but also on the whiskers, the threads or in the pores of the skeleton remote from the tube wall. As a certain minimum deposition of metal is necessary for the achievement of a good heat conducting connection, the porosity of the body is reduced as a result of the metal deposition, which leads to increased flow resistances. This is undesirable in many cases.
It is an object of the invention to provide a method whereby a very good heat conducting connection is achieved between the outer portion of the porous body and the tube wall, and yet the throughflow resistance is not increased excessively.